Systematic study of Δ\Delta(1232) resonance excitations using single isobaric charge-exchange reactions induced by medium-mass projectiles of Sn

The fragment separator FRS has been used for the first time to measure the (n,p)- and (p,n)-type isobaric charge-exchange cross sections of stable Sn112,124 isotopes accelerated at 1A GeV with an uncertainty of 3% and to separate quasielastic and inelastic components in the missing-energy spectra of the ejectiles. The inelastic contribution can be associated to the excitation of isobar Δ(1232) resonances and to the pion emission in s wave, in both the target and projectile nuclei, while the quasielastic contribution is associated with the nuclear spin-isospin response of nucleon-hole excitations. The data lead to interesting results, where we observe a clear quenching of the quasielastic component, and their comparisons to theoretical calculations demonstrate that the baryonic resonances can be excited in the target and projectile nuclei. To go further in this investigation, we propose to study the excitation of baryonic resonances, taking advantage of the combination of high-resolving power magnetic spectrometers with the Wide Angle Shower Apparatus (WASA) calorimeter. These new measurements will allow us to determine the momenta of the ejectiles and pions emitted in coincidence after the single isobaric charge-exchange collisions, providing us unique opportunities to study the evolution of the baryonic resonance dynamics with the neutron-proton asymmetry through the use of exotic radioactive ion beams

Alpha spectroscopy of purified beams of exotic nuclei at the FRS Ion Catcher

The FRS Ion Catcher (FRS-IC) is located at the final focal plane of the Fragment Separator FRS at GSI. The FRS-IC setup is well known for high-precision experiments with stopped exotic nuclei produced by projectile fragmentation and fission. The facility consists of the cryogenic gas-filled stopping cell (CSC), an RFQ-based beamline (DISTRICT), and a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). This paper illustrates how alpha spectroscopy performed at this facility has emerged as a promising tool to unveil the nuclear structure of exotic nuclei, i.e., half-live and decay energy measurements. First studies of that kind were performed on the decay chains of 218Rn, 219Rn, 221Ac, 220Fr, and 223,224Th produced by projectile fragmentation of 238U. The α decay energy measurements performed and the deduced Qα values confirm the known maximum at N= 128 and the values of Qα at N= 132 − 133 follows the predicted increasing in Qα values compared to the values for At isotopes at the same neutron number N. Further, the production rate ratio of the isomer to the ground state of 211Po was measured. It allows an estimate of the angular momentum distribution of 211Po fragments following fragmentation of 238U in a 9Be target at relativistic energies. In addition, the potential of mass-selected decay spectroscopy behind the MR-TOF-MS was demonstrated with short-lived 215Po ions (t1/2 = 1.78ms). This demonstrates that the FRS-IC is a reliable setup for α spectroscopy studies and related nuclear structure studies.peerReviewe

A novel method for the measurement of half-lives and decay branching ratios of exotic nuclei

A novel method for simultaneous measurement of masses, Q-values, isomer excitation energies, half-lives and decay branching ratios of exotic nuclei has been demonstrated. The method includes first use of a stopping cell as an ion trap, combining storage of mother and daughter nuclides for variable durations in a cryogenic stopping cell (CSC), and afterwards the identification and counting of them by a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). We utilized our method to record the decay and growth of the 216Po and 212Pb isotopes (alpha decay) and of the 119m2Sb isomer ( t1/2=850±90 ms) and 119gSb isotope (isomer transition), obtaining half-lives consistent with literature values. The amount of non-nuclear-decay losses in the CSC up to ∼10 s is negligible, which exhibits its extraordinary cleanliness. For 119Sb isotopes, we present the first direct measurements of the mass of its ground state, and the excitation energy and decay branching ratios of its second isomeric state (119m2Sb). This resolves discrepancies in previous excitation energy data, and is the first direct evidence that the 119m2Sb isomer decays dominantly via γ emission. These results pave the way for the measurement of branching ratios of exotic nuclei.peerReviewe

Twin GEM-TPC prototype (HGB4) beam test at GSI - a development for the Super-FRS at FAIR

The GEM-TPC detector will be part of the standard Super-FRS detection system, as tracker detectors at several focal stations along the separator and its three branches

Systematic study of Δ\Delta(1232) resonance excitations using single isobaric charge-exchange reactions induced by medium-mass projectiles of Sn

The fragment separator FRS has been for the first time used to measure the (n,p) and (p,n)-type isobaric charge-exchange cross sections of stable 112,124Sn isotopes accelerated at 1A GeV with an uncertainty of 3% and to separate quasi-elastic and inelastic components in the missing-energy spectra of the ejectiles. The inelastic contribution can be associated to the excitation of isobar Delta(1232) resonances and to the pion emission in s-wave, both in the target and projectile nuclei, while the quasi-elastic contribution is associated to the nuclear spin-isospin response of nucleon-hole excitations. The data lead to interesting results where we observe a clear quenching of the quasi-elastic component and their comparisons to theoretical calculations demonstrate that the baryonic resonances can be excited in the target and projectile nuclei. To go further in this investigation, we propose to study the excitation of baryonic resonances taking advantage of the combination of high-resolving power magnetic spectrometers with the WASA calorimeter. These new measurements will allow us to determine the momenta of the ejectiles and pions emitted in coincidence after the single isobaric charge-exchange collisions, providing us unique opportunities to study the evolution of the baryonic resonance dynamics with the neutron-proton asymmetry through the use of exotic radioactive ion beams.Comment: 14 pages, 9 figures. arXiv admin note: substantial text overlap with arXiv:2004.0640